Fuel dispensing system

ABSTRACT

A fuel dispensing system employing a dual rotor turbine flow meter is disclosed.

TECHNICAL FIELD

This invention relates generally to the field of fuel dispensingsystems, and, more particularly, to an improved fuel dispensing systemusing a dual rotor turbine flow meter.

BACKGROUND OF THE INVENTION

Fuel dispensing systems used for highway vehicles and marineapplications generally contain from one to eight flow meters andassociated valves and dispensing hoses. One or more displays indicatethe total delivered fuel quantity and the resultant sale price.Dispenser systems also provide one or more pumps to lift the fuel fromunderground storage tanks for delivery to the vehicle. The pumps areeither mounted within the storage tanks or separate therefrom.

Multiple fuel grades, usually differing octane levels for gasoline, areoften delivered from one dispenser. Diesel fuel is generally maintainedin a separate piping, metering and delivery system.

Meters are typically positive displacement meters which utilize multiplepistons on a crankshaft to measure the volume of fuel passingtherethrough. As fuel is forced through the meters, each piston isdisplaced thereby causing rotation of the crankshaft. Each stroke of thepiston displaces a precise quantity of fuel. For each stroke of thepiston, a number of electrical pulses is emitted from an encoding devicemounted to the end of the piston shaft. The number of pulses is used tocalculate the volume which has passed through the meter.

Piston meters as described do have some drawbacks. For example, sealsemployed in such meters are affected by the various chemical additivesin the fuels. Over time and because of new additives blended intogasoline, the seals may deteriorate. Piston meters also tend to be quitelarge and bulky. Thus, packaging of up to eight meters in a singledispenser creates a very large dispenser.

Further, as ambient conditions such as the air temperature of thetemperature of the fuel change, the internal dimensions of the pistonmeter also changes due to thermal expansion of the materials used tomanufacture the meter thereby resulting in errors in the delivered fuelquantities reported. There is no known method for correcting thisdimensional problem with piston meters.

While the inherent accuracy of the piston meter has been satisfactoryfor decades due to the relatively low price of fuel, as the price ofgasoline rises, the need for ever improved accuracy increases. Thepiston meter may not be able to meet this need.

Further, state of the art electronics now afford an opportunity topredict and alarm a central station when a failure of the meteringsystem is impending. However, piston meters do not have this capability.

Thus, there is a need for the use of a fuel dispensing system employinga new type of meter meeting these requirements. The present inventionmeets these needs.

SUMMARY OF THE INVENTION

It is an object of this invention to provide an improved fuel dispensingsystem having a meter which provides improved accuracy over pistonmeters.

It is a farther object of this invention to provide an improved fueldispensing system which is much smaller than a piston meter withcommensurate decline in the volumes of liquid contained therein.

It is still another object of this invention to provide an improved fueldispensing system which includes the ability to predict impendingfailures of the metering system.

It is another object of this invention to provide an improved fueldispensing system which is less sensitive to ambient conditions andwhich employs no seals to degrade performance over time.

Further objects and advantages of the invention will become apparent asthe following description proceeds and the features of novelty whichcharacterize this invention will be pointed out with particularity inthe claims annexed to and forming a part of this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be more readily described by reference to theaccompanying drawings in which:

FIG. 1 is schematic view of a fuel dispensing system using individualsystems for each separate grade of fuel;

FIGS. 2A and 2B are schematic views of a fuel dispensing system usingindividual system for each grade of fuel which dispenses the fuel fromone hose;

FIG. 3 is a schematic view of a fuel dispensing system which blends twogrades of gasoline to create multiple grades of fuel for dispensing viatwo separate meters for each of the two grades of gasoline;

FIG. 4 is a schematic view of a fuel dispensing system which blends twogrades of gasoline to create multiple grades of fuel for dispensing viaa single meter;

FIG. 5 is a schematic view of a mobile fuel dispensing system;

FIG. 6 is a timing diagram detailing the flow rate and totalizationroutines used in the present invention; and

FIG. 7 is a diagram showing the calculations used in the timing diagramof FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is, in its simplest form, the replacement of thepiston meters 12 and 42 previously described by a wide range, highaccuracy dual rotor flow meters 12 and 42. In the most preferredembodiment, such flow meters 12 and 42 use counter-rotating dual rotorsas described fully in U.S. Pat. No. 5,689,071 entitled “Wide Range, HighAccuracy Flow Meter” which issued on Nov. 18, 1997 to Ruffner et al.This patent is hereby incorporated by reference.

As described within U.S. Pat. No. 5,689,071, the wide range, highaccuracy flow meter is a dual rotor turbine flow meter which is upto 100times smaller than a corresponding piston meter and approximately 10times lighter. The dual rotor turbine flow meter is 2-3 times moreaccurate than a corresponding piston meter while the internal volume offuel-contained within the dual rotor turbine flow meter is severalhundred times less. Further, the dual rotor turbine flow meter has theability to predict impending failure by the changing ratio of rotorspeeds from the norm. The characteristics of the dual rotor turbine flowmeter allow the performance of same to compensate for changes intemperature, either ambient or the fuel itself The dual rotor turbineflow meter does not employ elastomeric seals and is therefore imperviousto gasoline additives.

As best seen in FIG. 1, in a system 5 generally limited to those withtwo or three differing grades of fuel, either with or without diesel,each individual grade is maintained in its own separate piping, meteringand delivery system 10. In such a configuration, a separate pump 11,dual rotor turbine flow meter 12 and control valve 13 is used for each,grade which is stored within its own tank 14 and dispensed through aseparate dispensing hose 16. No mixing of the various grades takesplace.

Since most dispenser systems 10 can be used from either of two sides,the number of systems 10 is usually a multiple of two. Meters 12, valves13 and pumps 11 are electrically connected to a point of sale displaycontroller 18 which selects the grade and displays the amount of fueldispensed and the sale price thereof.

As best seen in FIGS. 2A and 2B, in another system 20 multiple grades offuel are dispensed through a single hose 22 but maintained separablywithin its own tank 14, control valve 13 and meter 12. The volume ofpiping in the hose 22 must be kept below a preset limit usuallydetermined by a regulatory agency whereby the mixing of one grade withanother is minimal when switching between grades. A selector valve 17determines from which tank 14 the fuel is dispensed.

As best seen in FIG. 3, still another system 30 creates multiple, gradesof gasoline by blending two grades within dispensing system 30. Theconfiguration uses individual system 10 comprising pump 11, dual rotorturbine flow meter 12, control valve. 13 and tank 14 for each of the twostored grades of gasoline. A pair of mixing valves 32 regulate the rateof flow from the two tanks 14 to a predetermined ratio to deliver theblended grade selected by the consumer. Meter 12 within each separatesystem 10 is used to measure the quantity of each grade employed in theparticular blended grade and the sum of the two meters 12 is used tocompute the actual delivered quantity of fuel at display 18.

In still a fourth system 40 best seen in FIG. 4, a single dual rotorturbine flow meter 42 is used to measure all dispensed quantities offuel. The configuration uses two individual systems 46 comprising pump11, control valve 13 and tank 14 for each of the two stored grades ofgasoline. A single selector valve 44 joins the two systems 46 andregulates the rate of flow from either of the two tanks 14. Single meter42 is used to measure the quantity of delivered fuel to display 18. Thevolume of piping in system 40 after selector valve 44 must be kept belowa preset limit usually determined by a regulatory agency whereby themixing of one grade with another is minimal when switching betweengrades.

In still a fifth system 500 shown in FIG. 5, the system previouslydescribed in connection with FIG. 4 is mounted on a truck 520 formobility. System 500 is frequently used to fuel aircraft although it istypical of any mobile dispensing system. Physical replacement of atraditional piston meter 12 or 42 is as simple as removing the pistonmeter and inserting the dual rotor turbine flow meter therefore. Whilesmall changes in the plumbing may be necessary, such changes are wellknown in the art. If the system is designed from scratch, rather than areplacement of an existing piston meter, the smaller size of the dualrotor turbine flow meter allows for reducing of the overall system sizeand more optimal placement of the flow meters 12 and 42.

The major adjustments necessary to replacement of a piston meter to adual rotor turbine flow meter are to the electronics of the dispensingsystem. Typically, the electronics used in most dispensers today isadapted for use only with the electronic output of a piston meter. Theelectronics must be changed to accept the two pulse inputs from the dualrotor turbine flow meter, as well as the input from a temperaturesensor.

The dual rotor turbine flow meter is a flow rate measuring meter. Thus,in order to obtain the quantity of fuel flowing therethrough,inferential calculations must be used. The superior performance of thedual rotor flow meter is achieved by summation of the Strouhal Number(temperature corrected K-factor) of both rotors at the operating RoshkoNumber (temperature corrected frequency/kinematic viscosity) of eachrotor.

As described in U.S. Pat. No. 5,689,071, each rotor blade creates anelectrical pulse as it passes a sensor. Since the two rotors aredesigned to operate at different speeds, the frequency generated by eachrotor is also different. The different frequencies must be synchronizedinto a single rate computation over precise time intervals.

As best illustrated in FIG. 6, a 32 bit high frequency free runningtimer 50 is used as a clock. Typically, the clock rate is between 5-10MHz. A pulse train A is generated by the upstream rotor A. A pulse trainB is generated by the downstream rotor B. A counter 72 is used to counteach of the pulse trains A, B. A second counter timer 70 is used todetermine the sample period, preferably adjustable between 0.5 and 1.0MHz, which can be slower than timer 50. In seconds, the timer period ispreferably between 0.03 and 2 seconds.

When using a dual rotor turbine flow meter to quantify the amount ofliquid flowing therethrough, it is best to keep the sample period to aminimum which is determined by the computational speed of the processorsdoing the calculations. The faster the processor, the lower the minimumsample period. In the example given below, the sample period is 0.03seconds, or 30 milliseconds.

When the fuel begins to flow at time t=Nt₀, both rotors A, B begin torotate as liquid passes therethrough. Both rotors A,B will be at speedas determined by the flow rate within 3 milliseconds, well within the 30millisecond sample period. A first pulse 56 starts the timer which readsthe clock as t=Nt₁. In this illustrated example, first pulse 56 is inpulse train A. It will be apparent to those skilled in the art that theinitial pulse can also originate in pulse train B. At a first pulse 58generated by the other rotor B, the clock is again read at t=Nt₂.

At the end of the timer period at the first pulse generated by eitherpulse train A or B, the clock is again read at t=Nt₃ and at the nextpulse generated by the other rotor at t=Nt₄ where the timer is reset andanother timer period begins. Note that a 32 bit clock running at 7.5 mHzwill roll over every 572.5 seconds (i.e. all bits reset to 0) and thus,every time the clock is read a check must be made for such rollover.Likewise, the counters for each of the pulse trains are checked forrollover also though experience indicates that a 16 bit counter issufficient for such uses.

As shown in FIG. 7, the frequency f for each pulse train A, B is nowcomputed using the formula:

f_(A)=(Number of pulses in pulse train A during a first timerperiod-1)/[(Nt₃−Nt₁)/f_(cc)] where f_(cc) is the clock speed (i.e. 7.5MHz in this example).

f_(B)=(Number of pulses in pulse train B during first timerperiod-1)/[(Nt₄−Nt₂)/f_(cc)]

Note that FIG. 6 illustrates the number of pulses being 3. In actualuse, the number of pulses will vary between 6 to 50 depending on theflow rate. At the lowest normal operating flow rate, the meter frequencyis about 7 Hz; thus the timer period will be about 143 milliseconds.

To compensate for temperature variations, the fuel temperature issampled by a sensor 60, shown in FIG. 1, mounted on the meter. Atemperature viscosity characteristic of the fuel, preprogrammed into theprocessor, is used to determine the kinematic viscosity v₁ of the fuelat the operating temperature during the first period. The Roshko Numberfor each rotor is then calculated as follows:

Ro _(A) =[f _(A) /v ₁][1+3α(T ₁ −T _(R))

Ro _(B) =[f _(B) /v ₁][1+3α(T ₁ −T _(R))

where T_(R) is a reference temperature, typically 70° F. (20° C.) andα=linear coefficient of expansion of the meter material.

The calibration between each meter will yield a relationship between theRoshko Number and the Strouhal Number for each rotor. Using thisrelationship, and the calculated Roshko Number, the Strouhal Number iscomputed for each rotor:

St _(A1) =F(Ro _(A))

St _(B1) =F(Ro _(B))

The average flow rate for the initial period is calculated as follows:

q ₁=(f _(A1) +f _(B1))/[(St _(A1) +St _(B1))*(1+3α(T ₁ −T _(R)))

The quantity of fuel dispensed during the initial period is thencomputed as follows:

Q ₁ =q ₁(Nt ₄ −Nt ₁)

The calculations above are performed during each timer period as shownin FIG. 7. Thus, the total quantity of full dispensed is the summationof all quantities dispensed during all periods from the initial periodto the final period:

Q _(T) =ΣQ _(n)(from n=initial period to n=final period)

The above calculations permit the dispensing of fuel on a mass basiswhich is often useful in aircraft applications. In this instance, inaddition to programming in a temperature viscosity characteristic intothe processor, a density temperature characteristic is programmedtherein. Specifically,

m ₁ =Q ₁*ρ₁ where ρ=density of fuel in a given time period m_(T) =Σm_(n) (n=1 to n)

The calculations are similar thereafter.

It should be noted that errors do occur in the dual rotor turbine flowmeter in that the initial quantity dispensed between Nt₀ and Nt₁ isgenerally not counted. However, this error is balanced by extra pulsescounted during the stopping process at the end of the dispensing. Sinceboth rotors A, B have momentum, it takes a finite amount of time forthose rotors to actually come to a stop after the flow ceases. Thus,additional pulses are actually counted after flow ceases. These extracounts tend to cancel out the missing initial quantity.

For example, the start period of Q_(nt1)−Q_(nt0) is missed so that Q_(T)is understated by this amount. However, the period N_(t1)−N_(t0) is lessthan one pulse of the first rotor A, thus, typically, the times involvedare:

0.0003>P _(A) +P _(B)<0.1 sec whereby Q_(T) is understated by less than0.0005 Gal.

The above error is partially offset by the stop error wherebyQ_(nt+7)−Q_(nt+6) is overstated during the period P_(n+3) since aportion of the pulse on each rotor A,B is missed. However, during thestopping period, rotors A, B coast for a few additional pulses. Thus,the frequency is actually calculated artificially high. As a result, ifQ_(nt+7)−Q_(nt+6) is overstated by 2 pulses of 0.03 seconds each whichequals 6.6 Hz which is equivalent to a flow rate of 0.2 GPM. Thus, thestop error is addition about 0.00067 Gal. Combining the additive stoperror and the subtractive start error yields a total error of 0.00017Gal. The start/stop errors are usually quite small in comparison to thetotal volume of liquid dispensed.

In contrast, a piston meter provides stop/start errors which areadditive in that the quantity missed at both ends runs to favoring anundercount of fuel dispensed. Thus, the dual rotor turbine flow metertends to be more accurate than the piston meter.

Although only certain embodiments have been illustrated and described,it will be apparent to those skilled in the art that various changes andmodifications may be made therein without departing from the spirit ofthe invention or from the scope of the appended claims.

What is claimed is:
 1. A fuel dispensing system comprising: a dualcounter-rotating rotor turbine flow meter having a first rotor and asecond rotor for determining the volume of fuel dispensed, the firstrotor and the second rotor each having a plurality of rotor blades, thefuel dispensing system further comprising a point of sale displaycontroller adapted to accept a first pulse input and a second pulseinput from the dual rotor turbine flow meter and input from atemperature sensor, the first rotor and the second rotor operating atdifferent speeds, the first rotor having a first sensor mountedproximate thereto, the second rotor having a second sensor mountedproximate thereto, the first sensor creating the first pulse input asone of the plurality of rotor blades of the first rotor passes the firstsensor, the second sensor creating the second pulse input as one of theplurality of rotor blades of the second rotor passes the second sensor,a timer, a counter and a counter timer integrated into the point of saledisplay controller, the counter counting counts of the first pulseinputs and the second pulse inputs from the first sensor and the secondsensor, the counter timer being used to determine a first sample periodand a second timer period whereby said counts result in an integralnumber of first pulse inputs and the second pulse inputs, the countedfirst pulse input and the timer being used to determine the frequencyf_(A) of said first pulse input by the formula f_(A)=(Counted firstpulse inputs during the first timer period−1)/[(Nt₃−Nt₁)/f_(cc)] wheref_(cc) is the clock speed, Nt₁ being the timer reading at the start ofthe first time period which initially is when a first pulse is receivedfrom either of the corresponding sensors and subsequently is Nt₃ fromthe preceding time period, Nt₃ being the timer reading at the end of thefirst timer period, the counted second pulse input and the timer beingused to determine the frequency f_(B) of said second pulse input by theformula f_(B)=(Counted second pulse inputs during first timerperiod−1)/[(Nt₄−Nt₂)/f_(cc)], Nt₂ being the timer reading at the startof the second timer period which initially is when a second pulse isreceived from the other of the two sensors and subsequently is Nt₄ fromthe preceding time period, Nt₄ being the timer reading at the end of thesecond timer period, the point of sale controller calculating the Roshkonumbers for each rotor by the formulas, Ro_(A)=[f_(A)/v₁][1+3α(T₁−T_(R))and Ro_(B)=[f_(B)/v₁][1+3α(T₁−T_(R)) where T_(R) is a referencetemperature and T₁ is a temperature reading from the temperature sensor,and α=linear coefficient of expansion of the fuel and meter material andv₁ is the kinematic viscosity of the fuel at the temperature reading,the point of sale controller calculating the Strouhal numbers St_(A1)and St_(B1) from the following formulae, St_(A1)=f(Ro_(A)) and St_(B1)=f(Ro_(A)), and average flow rate q₁ for a timer period beingq₁=(f_(A1)+f_(B1))/[(St_(A1)+St_(B1))*(1+3α(T₁−T_(R))] and the quantityof fuel Q₁ dispensed during the timer period being Q₁=q₁ (Nt₄−Nt₁) andthe total fuel Q_(T) dispensed being calculated by summing Q₁ over allperiods.
 2. The fuel dispensing system of claim 1 wherein the timer is a32 bit clock running between 5 and 10 megahertz.
 3. The fuel dispensingsystem of claim 2 wherein the 32 bit clock runs at 7.5 megahertz.
 4. Thefuel dispensing system of claim 1 wherein the counter timer runs between0.5 and 1.0 megahertz.
 5. The fuel dispensing system of claim 1 whereinthe first timer period and the second timer period are between 0.03 and2 seconds.
 6. A fuel dispensing system comprising: a dualcounter-rotating rotor turbine flow meter having a first rotor and asecond rotor for determining the volume of fuel dispensed through thedual rotor turbine flow meter, the first rotor and the second rotor eachhaving a plurality of rotor blades, the first rotor and the second rotoroperating at different speeds, the first rotor having a first sensormounted proximate thereto, the second rotor having a second sensormounted proximate thereto, the first sensor creating the first pulseinput as one of the plurality of rotor blades of the first rotor passesthe first sensor, the second sensor creating tho second pulse input asone of the plurality of rotor blades of the second rotor passes thesecond sensor, a point of sale display controller adapted to accept thefirst pulse input and the second pulse input from each of thecorresponding sensors and input from a temperature sensor, a timer, acounter and a counter timer integrated into the point of sale displaycontroller, the counter counting counts of the first pulse inputs andthe second pulse inputs from the first sensor and the second sensor, thecounter timer being used to determine a first sample period and a secondtimer period, the counted first pulse input and the timer being used todetermine the frequency f_(A) of said first pulse input by the formulaf_(A)=(Counted first pulse inputs during the first timerperiod−1)/[(Nt₃−Nt₁)/f_(cc) where f_(cc) is the clock speed, Nt₁ beingthe timer reading at the start of the first time period which initiallyis when a first pulse is received from either of the correspondingsensors and subsequently is Nt₃ from the preceding time period, Nt₃being the timer reading at the end of the first timer period, thecounted second pulse input and the timer being used to determine thefrequency f_(B) of said second pulse input by the formula f_(B)=(Countedsecond pulse inputs during first timer period−1)/[(Nt₄−Nt₂)/f_(cc)], Nt₂being the timer reading at the start of the second timer period whichinitially is when a second pulse is received from the other of the twosensors and subsequently is Nt₄ from the preceding time period, Nt₄being the timer reading at the end of the second timer period, the pointof sale controller using the two frequencies to calculate the total fuelvolume being dispensed therefrom.
 7. A method for dispensing fuel usinga dual counter-rotating rotor turbine flow meter having a first rotorand a second rotor for determining the volume of fuel dispensed, thefirst rotor and the second rotor each having a plurality of rotorblades, the method comprising the steps of: operating the first rotorand the second rotor at differing speeds, generating a first pulse inputas one of the plurality of rotor blades of the first rotor passes afirst sensor mounted proximate to the first rotor, generating a secondpulse input as one of the plurality of rotor blades of the second rotorpasses a second sensor mounted proximate to the second rotor, countingthe first pulse inputs and the second pulse inputs, determining a firsttime period providing as integral number of first pulse inputs,determining a second time period providing an integral number of secondpulse inputs, calculating the frequency f_(A) of said first pulse inputthe formula f_(A)=(Counted first pulse inputs during the first sampleperiod−1)/[(Nt₃−Nt₁)/f_(cc)] where f_(cc) is a clock speed, Nt₁ beingthe time at the start of the first time period defined initially when afirst pulse is received from either of the corresponding sensors andsubsequently is Nt₃ from the preceding time period, Nt₃ being the timerreading at the end of the first timer period, the counted second pulseinput calculating the frequency f_(B) of said second pulse input by theformula f_(B)=(Counted second pulse inputs during first timerperiod−1)/[(Nt₄−Nt₂)/f_(cc)], Nt₂ being the timer reading at the startof the second timer period which initially is when a second pulse isreceived from the other of the two sensors and subsequently is Nt₄ fromthe preceding time period, Nt₄ being the timer reading at the end of thesecond timer period, calculating the Roshko numbers for each rotor bythe formulas, Ro_(A)=[f_(A)/v₁][1+3α(T₁−T_(B)) andRo_(B)=[f_(B)/v₁][1+3α(T₁−T_(R)) where T_(R) is a reference temperatureand T₁ is a temperature reading from the temperature sensor, andα=linear coefficient of expansion of the fuel and meter material and v₁is the kinematic viscosity of the fuel at the temperature reading, thepoint of sale controller calculating the Strouhal numbers St_(A1) andSt_(B1) from the following formulae, St_(A1)=f(Ro_(A)) andSt_(B1)=f(Ro_(B)), and average flow rate q₁ for a timer period beingq₁=(f_(A1)+f_(B1))/[(St_(A1)+St_(B1))*(1+3α(t₁+T_(R))) and the quantityof fuel Q₁ dispensed during the timer period being Q₁=q₁ (Nt₄−Nt₁) andthe total fuel Q_(T) dispensed being calculated by summing Q₁ over allperiods.